1. Field of the Invention
The present invention relates to an energy harvesting apparatus and method, and more particularly, to an energy harvesting apparatus and method for rapidly tracking a maximum power point of a device for converting vibration energy into power or a piezoelectric device.
2. Description of the Related Art
Low-carbon green growth is policy keynote of major developed countries. As one of methods for realization of this, low-power or non-power semiconductor design has become a big issue. Energy harvesting technology has draw attention as a very important factor for the low-power or non-power semiconductor design and the utility of energy harvesting technology has also remarkably increased by virtue of the development of various device technologies for converting energy such as light, vibration, heat, etc. into electrical energy. In addition, due to introduction of various mobile devices and wireless sensor nodes, users' requirements for energy harvesting technology have been on rise. It is necessary to effectively transfer energy harvested via the energy harvesting technology and to simultaneously lower power of a device for controlling the effective energy transfer.
In general, an energy harvesting circuit includes a harvester for producing power, a rectifier for converting generated energy into a direct current (DC) component, and a charging circuit for storing energy output from the rectifier in a battery or a high capacitance of capacitor. The harvester includes a piezoelectric device or a device for converting vibration energy into power. The device has a maximum power point that is determined according to an input amplitude and frequency.
Accordingly, in order to increase energy harvesting efficiency of the energy harvesting circuit, it is necessary to match a voltage and current between an output terminal of the rectifier and an input terminal of the charging circuit to the maximum power point. In this case, the maximum power point corresponds to a time point when half of an open circuit voltage is reached.
Conventionally, in order to find the maximum power point, a method (e.g. a Perturb & observe method, a Hill-climbing method, or the like) for tracking the maximum power point along with slight change in a voltage and current between an output terminal of a rectifier and an input terminal of a charging circuit or a method for tracking the maximum power point by opening a switch disposed between the output terminal of the rectifier and the input terminal of the charging circuit and then measuring an open voltage generated from the output terminal of the rectifier is mainly used.
In this conventional method, time corresponding to several tens to several hundreds of periods is taken to track the maximum power point. Accordingly, conventionally, power loss occurs during tracking of the maximum power point and there is a limit to apply the conventional method to an energy harvesting system with high variability of power harvested by a harvester.